Current Human Impacts

Bay Area wetlands offer a wide range of ecological services. They provide wildlife habitat for over 500 species of wildlife, 105 of which are threatened and 23 of which are endangered. They also help control flooding by holding and absorbing excess water, provide ground-water recharge, and can even contain pollutants in the flooded soil. Unfortunately, Bay Area wetlands are currently threatened by human activities such as pollution, climate change, freshwater diversion, invasive species, and shoreline urbanization. The severity of these impacts are related to population growth: the Bay Area population is expected to grow another 15 percent to 8.1 million by 2020.

Today, pollution in the Bay Area poses serious threats to the region’s wetlands. Manmade pollution comes from car exhaust, pet waste, trash, household toxins such as fluorescent light bulbs that contain mercury, and more. Pollution that comes from non-point sources is particularly problematic because it is difficult to control and contain its effects. Mercury and Polychlorinated Biphenyls (PCBs) that come from old mining activities adversely affect the wetlands since they contaminate water and poison sensitive species. When not disposed of correctly, these pollutants wash into storm drains and flow into the Bay. Run-off caused by improper waste treatment methods also pollutes wetlands with pesticides used in agriculture and chemicals from industrial activity.

Anthropogenic climate change also affects the wetlands by changing temperatures and water quality, which contributes to further decreases in species diversity. As the planet warms, sea levels increase (water expands when its hot, in addition to melting ice and glaciers), which puts pressure on many species. Climate change can also lead to changes in runoff patterns that bring more fresh water into the Bay during the winter but less in the spring and summer. Scientists predict that this will cause parts of the Delta to become saltier. This will pose a serious problem since many plants and animals are not adapted to saltier conditions. Humans’ demand for water is also contributing to the diversion of freshwater in the Delta. Freshwater supplies are pumped from the area to be used by 22 million Californians. Unfortunately, 95% of the Delta’s diverse freshwater plant habitat has already been lost. In addition, human-introduced nonnative species damage Bay Area wetland ecosystems. Plants such as Australian bent grass and iceplant can outcompete native vegetation and take over large areas, which leads to a decrease in species diversity.

Finally, urbanization is impacting Bay Area wetlands. Wetlands usually migrate inland when sea levels rise, but plants and animals are currently running out of available space because of Bay Area urban development. Table 10 lists the types and extents of areas that are currently not viable, viable but will cause property loss, and viable for wetland migration in the San Francisco Bay Area. Developed areas are considered to be not viable for wetland migration (this includes all areas with high to low intensity development). These areas constitute 35 square miles of land in the Bay Area. Although 53 square miles are considered viable, 35 square miles is a lot of space that is no longer available to wetlands. It is also reasonable to predict that people may not want to pay for the property damage that would come from making another 4.9 square miles available for wetland migration. Rises in sea level paired with the constraints of Bay Area urbanization put serious environmental pressure on the ecosystem, trapping existing wetlands within a smaller and smaller inhabitable range.